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London (CNN)Police in London say they have foiled a second active terror plot in 24 hours, after arresting six people in raids across the British capital and southeast England.

A woman shot by police in the latest counterterrorism investigation remains in a serious but stable condition. The investigation is LPolice said the operation late Thursday night was not related to anearlier arrest near the British parliament,where officers detained a man armed with knives on suspicion of planning a terror attack, in what Deputy Assistant Commissioner Neil Basu described as "an extraordinary day" in London.

"Due to these arrests that we have made, I believe that we have contained the threats that they posed," he said.

A man is arrested in central London on Thursday on suspicion of terror offenses.

The woman was shot Thursday evening as armed officers entered a house in Willesden, in the city's north-west. Six other suspects have been arrested in connection with the raid, Basu told reporters Friday.

He confirmed that police believe they have foiled an active terror plot with the arrests.

Witness Sean Rahilly said he was at St Mary Magdalen Church when he heard gun shots just before 7 p.m. local time. "Everyone outside the church was confused (about) what was happening. Within one minute of the gun shots armed police showed up," he said

Police said that intensive work was underway to contain the terror threat in the UK. "I wanted to reassure the public that our increased activity to combat terrorism over the last two years continues -- both by police and security services. Activity continues around the clock to identify and stop these threats and we are making arrests on a near daily basis," Basu said.

Hospital guard

The injured woman, who is in her 20s, was taken to the hospital, where she remains under police guard. She has not yet been arrested due to her condition, Basu said. Police are monitoring her condition closely.

"An armed entry was necessary due to the nature of the intelligence that we were dealing with, and involved armed officers firing CS (teargas) into the address," Basu said.

Six people have been arrested in connection with that investigation, he said, five at or near the address in Willesden and one in Kent, a county southeast of London. At least four were arrested for alleged terrorism-related offenses.

Police continue to search three addresses in London, one of them the Willesden house, he said.

An independent investigation has been launched into the operation, Basu said, as is routine when a person is shot by police. It is unusual for British police officers to fire weapons and very unusual for a woman to be shot.

Security boosted

In the earlier incident, armed officers from the Metropolitan Police's counter-terrorism command unit arrested a 27-year-old man, a few meters from the scene of a terror attack last month that leftfive people and the attacker dead.

Source: CNN

Man arrested near UK Parliament00:33

Witnesses said the man was pinned to the ground on Parliament Street, within sight of the Houses of Parliament and an array of British government buildings.

Downing Street, the official residence of the British Prime Minister, is a few minutes' walk away. Prime Minister Theresa May was not at the premises during the arrest, her office told CNN.

Forensics officers examined the scene outside the London Underground station at Westminster and recovered the suspect's backpack and at least two knives. He was arrested on suspicion of possession of an offensive weapon and on suspicion of the commission, preparation and instigation of acts of terrorism, police said.

Two searches continue at addresses in London as part of that investigation, Basu said.

"With the attack in Westminster on 22 March so fresh in people's minds, I would like to reassure everyone that across the country officers are working round the clock to identify those people who intend to commit acts of terror," he said.

"After that attack, we increased the number of officers on duty patrolling at key locations -- and that continues as we police against the backdrop of a severe terrorist threat.

"There are constant acts of immense bravery by officers -- armed and unarmed -- those that the public see when our officers run towards danger, just like yesterday, but a huge amount of unseen work that the public will never know about from us and our brilliant security services